warBondDiceSides = determines the dice used during warbond rolling, I believe -1 default setting is equal to whatever "diceSides" is set to (top of xml), assuming it's different from d6. (Although @beelee would be correct as to -1 typically indicating unlimited, just not for this case.)

Theoretically you can create a super tech, with abilities from many techs all in one tech . So "Effects from multiple techs are added together." is a correct statement.

Theoretically you can create a super tech, with abilities from many techs all in one tech . So "Effects from multiple techs are added together." is a correct statement.

I understood "Effects from multiple techs are added together." (from other options) to mean that if there are several techs that mod the same thing, those mods are added together, as opposed to a situation where only the lowest or highest mod is used.
"Effects from multiple techs are added together." for warBondDiceSides does not make sense, if you added dice sides together the hit ratio would go down!
I suspect that in the case of multiple techs it would select the lowest warBondDiceSides of the techs.